Nocturnal exacerbations of asthma are frequent and serious events. The mechanisms of nighttime asthma are not fully established; however, sleep and circadian variations in epinephrine (EPI) and cortisol (CORT) appear to be important factors. This study will determine the influence of sleep and circadian variations in EPI and CORT on nocturnal airway obstruction and inflammation in asthma and the potential role of enhanced generation of cytokines in the process. By studying subjects at 4:00 AM and 4:00 PM while awake and asleep, the independent and interactive contribution of sleep and circadian rhythm will be determined. We hypothesize that sleep and circadian decline in EPI and CORT have an independent and interactive role in causing sleep-related asthma.